I think the key to the textpattern thread is this post:
"Jason kindly checked out the error.log and unfortunately found no errors relating to fcgi or apache. The only entries in there are 'not found' links relating to my old blog which ran textpattern e.g the url http://www.mpet45.co.uk/article/559/whatever which generates an error in RoR given that there is no such url anymore."
I was getting a bunch of 500 errors due to not having a robots.txt file. Any time a request comes in that you have no route for, and the url doesn't fit the default route, you'll get 500 errors.
I also got them from my 500 page itself as I had a stylesheet linked to it using a relative url. When the 500 page was generated from other than the top level of the site, the stylesheet could not be found and that generated another 500 error. (Changing it to /stylesheets/my.css fixed it -- that is, adding the leading slash.)
In the end, many, many of the 500 errors are tracked down to some little thing in the application. However, I also found a new fcgi_handler yesterday that I've been using the last 24 hours and it seems to eliminate those last few. At least I haven't seen once since installing it. It really seems stable and fast:
The processes seem to get the shutdown notice and are able to gracefully exit when they are not in the middle of a process (which I think is what would happen in the prior version).
I think with the old handler, once a process got broken in some way it didn't go away until it was in the middle of another request. I think this handler sets them to expire before handling the request so a good process can take over.
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